Tap switch



July 17, 1956 L. w. PARKER 2,755,364

TAP SWITCH Filed May e, 1953 IZL INVENTOR LOUIS W. PARKER ATTORNEYS United States Patent TAP SWITCH Louis W. Parker, Great Neck, N. Y. Application May6, 1953,"Serial'No. 333,267 v15 C a ms- .2 0-1 3) The present invention relates to switches and circuit coupling devices, and is more particularly concerned with a switch or coupler construction "wherein a rotatable screw is utilized for selective switching'purposes.

'In the past, rotary switches or selective couplers utilizing a rotatable screw for circuit coupling or tapping purposes have been subject'to a nu'mber of pronounced disadvantages. Ordinarily these switches comprise 'a body member, having stationary electrodes, and a rotatable screw coaxial with :said body and carrying movable cont'acts. 'By rotating, advancing, or retarding the screw within the said body, the movable contacts mak'e selectiv'e e'nga gement with-the stationary contacts to therebyeiiecta desired external circuit continui-ty. In general, the screw member itself has not been utilized as-a contact tnember, but has physically carried auxiliary contacts in the form of lugs orspring mernb'ers attached to the screw, or in the form of travelling contacts *freely moving along the screw, these free contacts being 'adv'anced'by rotation of the screw. Moreover, in prior art devices, the 'body structure has been of such construc tion that a relatively slight wearing or distortion "of parts results in faulty operation of the switch. Thus, if the threads of the main scriew member should become worn, or if one of the contacts, either movable =orstationa'ry, shohld somehow become bent, the switch may fail to operate atone or even several positions of "screw rotation.

It has also been found that .prior art tap switches a're so constructed that, even when the component elements anoothe'rwise normal physically there is insufficient force between the fixed and movable switch contacts to prevent intermittent opening of an external circuit due to jarring or vibration of the switch. Again, this force befor {the t ur t-he'r reason that prior art 'tap switches, of the -'b'road general type contemplated herein, have ordinarily been too l'arge to mount adjacent the circuit components in electronic equipment, such priorartswitches have tons- 'ton'iarilsy been mounted directly 'on the front panel or the said equipment. This in turn has necessitated the use of rlativehy dong leads between the switch :and circuit components, with the very undesirable possibility of parasitics and excessive reactive loading normally attending -such circuitry disposition.

:It is accordingly an object iof this invention to .pro-

a tap switch wherein "a screw member is caused to be advanced-stir retarded within a ifixed body member, the

of the said equipment. --constructed that it may be fabricated with relatively small ice screw member itself acting as a contact for providing continuity betweenselected portions of the body member. 'ln'this respect, I have provided a body member having a plur'ality of conductive portions separated from one another by insulating portions, sothat advancement or re'tarding-of aconductive scre'w directly couples selectedonesof said conductive body portions, or taps, together through said screw.

It is a further object of this invention to provide a 'tap switch wherein a plurality of external circuit components may be coupled respectively to individual conductive members'of a switch'body portion, and wherein advancement of a screw withinsaidbody portion effects a highly compressive and "therefore positive engagement of the screw and conductive members. My switch has accordingly separated the said individual conductive members by'a plurality of physically compressible insulating members so that,'in one embodiment of my invention, advancement of "the screw causes said insulating members to be compressed to less than their normal dimensions, the individual conductive members thus making contact with the screw member under considerable contacting pressure. In accordance with still another embodiment of my invention, the physically compressible members are even further compressed by the means normally maintaining the relative positions of conductive and insulating members, so -that=advancem'ent of the screw permits some expansion of the insulating member with the same a a ta es de c i d h r n- Still a-fUrther-pbject of the present invention resides in the provisionof asw-itch unit which may be located adjacent circuit components in electronic equipment, and which may be controlled accurately by flexible shaft means extending between the switch and the front panel In this respect, my switch is so dimensions, and the switch construction further necessitates a full turn of the screw member to advance the screw from oneof the conductive body portions to the 'next conductive portion. Any inaccuracy resulting from the use of flexible shafts is therefore made unimportant in the switch operation.

it is a further object of this invention to provide a switch wherein a rotatable screw, in engaging conductive body members, provides plural contacts between the said screw and said body members, and wherein balanced pressure is exerted upon said conductive body members and upon insulating members separating said conductive body members from one another. In providing for this object, my tap switch utilizes a rotatable screw contactor having multiple threads. Further, since normal operation of my switch results in the compression of the separating insulating members with a resultant actual decrease in "spacing between adjacent conductive body portions of my switch, I have so fabricated the screw contactor of my switch that a portion of the threading has a larger pitch than the remainder thereof, whereby theengagement'of the'sc'r'ew member and conductive body portions is greatly facilitated.

These and other objects and advantages of my invention will be more readily seen from the following description and accompanying drawings in which:

Figure -l is a cross-sectional view of a preferred embodiment of iny switch unit, and

Figure 2"is a detail view of a portion of the screw member utilized in the switch of Figure 1.

Referring now to Figure 1, it will be seen that my switch comprises a plurality of conductive members '11 separated respectively from one another by insulating portions :13 and i3a. The said members 11, 13 and 13:: preferably take the form of a stack of square washers, and this stack is suitably held together between face plates l and 20 by appropriate structure (not shown). The conductive washers 11 are threaded internally to permit engagement with an elongated screw 14 passing through the said stack and coaxial with the longitudinal axis of the stack. The insulating washers 13 and 13a are not threaded internally, but take the form of hollow squares of insulating material having a sufficiently great inside dimension to permit ready passage of the screw 14 under all conditions of switch operation. It is to be understood, of course, that the washers 11, 13, and 13a may take the shape of a circle, hexagon, or any other appropritae configuration.

In forming the stack 111313a, a quantity of metal washers 11, of equal thickness, is first stacked and marked so that, after disassembly, they may be reassembled at a later time in the same relative position to one another. After having thus stacked and marked the washers 11, the stack is held firmly together and is threaded internally. In the preferred embodiment of my invention shown in Figure l, the contactor screw member 14 is provided with double threads, and if this structure is to be utilized the internal threading of the stack should be effected, of course, by a double-threaded tap. After having thus threaded the stack of washers 11, the stack is separated and every second washer is reassembled in a further stack with insulating squares 13 between individual washers 11. As may be seen, therefore, and in order to provide proper thread engagement in the completed switch, only one-half of the washers 11, in the original stack of metal washers, is utilized in providing the said further stack 11-13.

The insulating washers 13 are formed of such material that they may be fairly readily compressed. One such material which has been employed with success is silicon rubber, but it is to be understood that any other material having both insulating and resilient compressibility characteristics may be employed. The insulating washers 13 have a thickness, under moderate pressure, of about to 20% greater axial dimension than that of an individual metal washer 11. One of said insulating washers 13 under such moderate pressure only (which pressure is caused by the means holding the stack together) is shown at 13a. As the screw 14 is advanced within the stack, and as the said screw engages each new conductive washer 11, the said new conductive washer is physically pulled back along the axis of screw 14 until it assumes the same relative position, with respect to the preceding metal washer 11, which the two washers occupied in the original stack of washers 11. Because of this pulling back or cinching of each metal washer, due to the increased thickness of the interposed insulating washer, the said interposed insulating washer is co1npressed to less than its normal thickness, as at 13, and thereby exerts considerable force on each of the metal washers contiguous therewith, causing a positive engagement between the said metal washers 11 and the screw 14.

A consideration of possible actual dimensions will facilitate an understanding of the foregoing switch operation. Thus, if each of the metal washers 11 has a thickness of 30 mils, every second washer of the original stack is replaced after tapping, with a compressible insulating washer having a thickness, under moderate pressure, of about 35 mils. Clearly such an arrangement displaces, along a longitudinal axis, the various internal threads of washers 11 from the relative positions they occupied in the original stack. However, as the screw 14 is fed through the stack 11--13, screw engagement with each 4 state. In addition to the foregoing structure, a large washer 15 of compressible material is provided at one end of the stack 11-13 to take up differences in length during operation of the switch.

A plurality of electrical leads 12 are coupled, respectively, between the various conductive washers 11 and external circuitry. As the screw 14 advances within the stack 1113, electrical continuity is established between adjacent leads 12, through their complementary washers 11 and the portion of screw 14 lying between said washers. Although the screw 14 only provides contact between the various washers 11 and their associated leads 12, it is further contemplated that a further electrical contact may also be made to the screw 14 itself, either through face plate 10, or through appropriate slip ring structure. The precise configuration of electrical connections will of course depend on the circuitry requirements.

In order that balanced pressure may be applied to the various washers 11 and 13 during switch operation, the screw 14 is cut with multiple threads. This screw configuration furthcr provides for multiple points of contact between the screw 14 and conductive washers 11. It has been found that a double thread on screw 14 operates very satisfactorily; in practice there may be sixteen such double threads per inch on a 71 inch rod, when washers 11 having a thickness of 5 inch are utilized. Again, however, any number of threads larger than two may be utilized effectively in the practice of my invention. The use of such a multiple threaded screw, and compressible washers between stationary contacts, results in several definite points of pressure between the screw and contacts, a feature not present in prior art tap switches. It has been 'found that this pressure is very substantial over several square millimeters of area, thus insuring positive contact between screw 14 and washers 11 under all practical operating conditions. In addition to this very substantial advantage, it will be seen that all contacts are self cleaning due to the wiping effect of the screw 14 during operation. It has been further found that the current carrying capacity of my switch is several times that of prior art switches of the same size.

Inasmuch as the metal washers 11 are separated from one another by distances greater than normal, because of the increased thickness of compressible washers 13, the forward end of screw 14 is provided with a slightly expanded thread to facilitate the screw 14 catching the internal threads of each new washer 11. This feature is shown in greater detail in Figure 2. Thus, the normal thread pitch is designated as a, while a larger thread spacing "b is provided at the outer end of screw 14. The spacing b has been much exaggerated in Figure 2, for purposes of clarity. Also, for purposes of clarity, one full turn of the thread has been shown as expanded. It must be emphasized, however, that in actual practice only the last A or $6 of the thread need be expanded to provide proper operation and ready thread engagement.

The above described embodiment of my invention has been predicated upon the assumption that the means holding metal washers 11 and compressible washers 13 within the stack is so selected that compressible washers 13 are normally of a slightly greater thickness than that of washers 11. In accordance with a still further embodiment of my invention hosvever, a slightly difierent arrangement is utilized. The physical relationship of the parts of my switch remains the same as has been shown in Figure 1, and the steps in the switch manufacture are again as described previously. However, in assembling the stack 1113, the washers 13 are so held within the stack that they are compressed to an even greater degree and the compressible washers 13 are made to have a slightly smaller thickness than that of conductive washers 11. Again, as the screw 14 is advanced within the stack 11-13, there is a physical translation of wsshers 11 whereby the thickness of insulating washers 13 is made to become equal, as before, to that of conductive washers 1-1. However, "inasmuch as compressible washers 13 originally'iz-ad-a thicknessin the sta'ok less than that of washers 11, advancement of screw 14 results in a pushing apart, rather than a "pulling together, of the conductive washers 51 1. .Largeseompressible washer .15 will again take up differences in .length of'the :stack and the same considerations as to tension between conductive washers 11 and screw 14 will apply. It should be noted, however, that in addition to the advantages already described, this latter embodiment of my invention has the further advantage that, since screw 14 tends to push washers 11 apart rather than pull them together, the end of screw 14 need not have the expanded thread shown in Figure 2. Thus, since a normal multiplethread screw may be utilized and since no expanded thread considerations enter the picture this latter embodiment of my invention is even more economical to manufacture than that previously described.

While the tap switch of my invention finds great utility when made as a relatively large unit, the switch construction is such that it may be made of sufficiently small size to permit location directly adjacent a circuit component or components in electronic equipment, instead of on the front panel of such equipment as has been customary. Tuning may then be effected through a short flexible shaft coupled to screw 14 and extending through the said front panel. Since each tap of my switch requires a full turn of screw 14, any inaccuracy resulting from the use of such a flexible shaft has no effect in proper and accurate switching operations.

Having thus described my invention, I claim:

1. A switch comprising first and second conductive washers each of which has a first thickness, said conductive washers being separated by an insulating washer normally having a second and different thickness, said insulating washer being formed of a resiliently com pressible material and being under compression between said conductive washers, said conductive washers being threaded internally, and a screw member in selective thread contact with said conductive washers and rotatably advanceable from said first to said second conductive washer, advancement of said screw member from said first conductive washer to said second conductive washer causing a physical translation of one of said conductive washers with respect to the other thereof with a resultant change in the degree of compression of the interposed insulating washer whereby said second thickness is made equal to said first thickness.

2. The switch of claim 1 in which said second thickness is originally greater than said first thickness, advancement of said screw causing an increase in the degree of compression of said insulating washer.

3. The switch of claim 1 in which said second thickness is originally less than said first thickness, advancement of said screw causing a decrease in the degree of compression of said insulating washer.

4. The switch of claim 1 wherein said screw member has a multiple thread, one end of said thread having a slightly expanded pitch to facilitate thread engagement between said screw, as it is advanced, and said conductive washers.

5. A tap switch comprising an elongated stack of conductive elements, a plurality of insulating elements of resiliently compressible material interposed respectively between said conductive elements, said conductive elements each having the same thickness along the longitudinal axis of said stack and each of said insulating elements having a somewhat greater thickness under moderate pressure than that of said conductive elements, said conductive elements being internally threaded to engage a screw member which may be advanced along the axis of said stack, the pitch of threads of said screw member and of said conductive elements being such that as said screw member is advanced from one of said conductive elements to the next-adjacent conduetiv'e e lement, said next adjacent conductive element is physically translated to compress the interposed insulating element.

6. The switch of claim 5 including a relativel-y iarge compressible member adjacent one end of 'said sta'ck, said compressible mem'be'r compensating for changes in length of said stack due to longitudinal movem'entof said screw.

7. The switch of claim 6 in said conductive elements and said screw member havemultipl'e threads.

8. The switch of claim 7 in which the thread pitch at one end of said screw member is expanded.

9. The method of making a switch which comprises assembling a stack of rigid washers, threading said washers internally, disassembling said stack, removing one of said rigid washers therefrom, replacing said removed rigid washer by a resilient washer of different thickness, reassembling the stack, and threading a screw member into said internally threaded washers.

10. The method of making a switch which comprises assembling a stack of rigid washers, threading said washers internally at a predetermined thread pitch, disassembling said stack, removing every second one of said rigid washers therefrom, replacing said removed rigid washers by resilient washers of different thickness, reassembling the stack, and threading a screw member having said predetermined thread pitch into said internally threaded washers.

ll. The method of making a switch which comprises assembling a stack of rigid conductive washers, threading said washers internally at a predetermined thread pitch, disassembling said stack, removing every second one of said rigid conductive washers therefrom, replacing said removed rigid washers by washers of an insulating and resiliently compressible material having an unstressed thickness greater than the thickness of said removed rigid washers, reassembling the stack, and threading a screw member having said predetermined thread pitch into said internally threaded washers.

12. A switch comprising a stack containing a first set of rigid washers and a second set of resilient washers, the washers of said first and second sets being disposed in said stack in alternating sequence, the washers of one of said sets being threaded, and a screw member in selective thread engagement with said threaded washers whereby said screw member may be selectively advanced and withdrawn with respect to said sets of washers, the unstressed thickness of said resilient washers when said screw member is withdrawn being different from the separation of said rigid washers when said screw memher is advanced into engagement with said threaded washers.

13. A switch comprising a stack containing a set of conductive washers and a set of insulating washers, the washers of said sets being disposed in said stack in an alternating sequence, the washers of one of said sets being rigid and the washers of the other of said sets being resilient, the washers of one of said sets being threaded, and a conductive screw member in contact with selective ones of said conductive washers, the unstressed thickness of said resilient washers when said screw member is withdrawn being different from the separation of said rigid washers when said screw member is advanced into engagement with said threaded washers.

14. A switch comprising a stack containing a plurality of rigid washers and a plurality of resilient washers, the said pluralities of washers being contiguous with one another in alternating sequence, the Washers of one set being threaded internally, means for limiting rotational movement of said threaded Washers, and a threaded screw member rotatable within said stack in contact with selective ones of said threaded washers, the thickness of said resilient washers when said screw member is withdrawn from said stack being greater than the separation of said rigid washers when said screw member is advanced into engagement with said threaded washers,

the thread of said'screw member having an expanded pitch at its advancing end to facilitate thread engagement with said threaded washers.

15. A switch comprising a set of conductive members, a set of insulating members respectively interposed between said conductive members, and a connecting member adapted to be advanced into selective contact with said conductive members, the members of one of said sets being resilient and being subjected to deformation References Cited in the file of this patent UNITED STATES PATENTS Carr Mar. 2, 1909 Schelke July 29, 1952 

